Cell Replication and Variation

Binary Fission: rapid reproduction producing a new organism from parent

• Interphase - Cell cycle where cell spends most of life • Prophase - chromosomes condense so visible - sister chromatids held together by centromere; nuclear membrane breaks down • Metaphase - homologous chromosomes align in middle of cell via centromere • Anaphase - spindle fibres (from centrioles) pull centromere towards ‘poles’ of cell - splitting sister chromatids • Telophase - nuclear membrane reforms around chromosomes at each pole • Cytokinesis - cytoplasm divides and two nuclei (forming two cells) - not considered part of mitosis

Diploid = 2n = 46 (mitosis) Haploid =n = 23 (meiosis)

Same as mitosis but repeats Prophase I - crossing over Metaphase I - pairs independently assorted ( each side of equator had random number of maternal and paternal chromosomes)

Independent assortment: assortment of chromosomes in meiosis II. Each chromosome assorted independently of other resulting in variation of possible chromosomes in each cell. Random fertilisation: One ovum will mature, and millions of sperm cells will mature offering vast variety in chromosomal combinations)

Production of gametes

oogenesis - produces one haploid ovum - the other three are degenerate, oogenesis precursor: oocyte, discontinued process - tightly regulated beginning before birth and is only completed after fertilisation Both - involve formation of haploid gamete cells from an original diploid cell, precursor cells undergo mitotic division before meiosis can occur, hormones play a crucial role in initiating and controlling both processes Spermatogenesis - produces 4 x haploid spermatozoa cells, spermatogenesis precursor: spermatocyte, continuous process - begins at puberty

Refer to Table 1 pg217 of the Textbook